Relationship of urinary phthalate metabolites with serum thyroid hormones in pregnant women and their newborns: a prospective birth cohort in Taiwan

Endocrine Disruptors in Pregnancy: Effects on Mothers and Fetuses-A Review

Background/Objectives: Endocrine disruptors are ubiquitous agents in the environment and are present in everyday consumer products. These agents can interfere with the endocrine system, and subsequently the reproductive system, especially in pregnancy. An increasing number of studies have been conducted to discover and describe the health effects of these agents on humans, including pregnant women, their fetuses, and the placenta. This review discusses prenatal exposure to various endocrine disruptors, focusing on bisphenols, phthalates, organophosphates, and perfluoroalkyl substances, and their effects on pregnancy and fetal development. Methods: We reviewed the literature via the PubMed and EBSCO databases and included the most relevant studies. Results: Our findings revealed that several negative health outcomes were linked to endocrine disruptors. However, despite the seriousness of this topic and the abundance of research on these agents, it remains challenging to draw strong conclusions about their effects from the available studies. This does not allow for strong, universal guidelines and might result in poor patient counseling and heterogeneous approaches to regulating endocrine disruptors. Conclusions: The seriousness of this matter calls for urgent efforts, and more studies are needed in this realm, to protect pregnant patients, and ultimately, in the long term, society.

Phthalate exposure during pregnancy and its association with thyroid hormones: A prospective cohort study

Phthalate esters (PAEs) possess endocrine-disrupting properties. Studies in humans have indicated that in utero phthalate exposure affects maternal thyroid hormones, which are essential for fetal growth and development. However, these studies also reported inconsistent results on the relationship between phthalates and thyroid hormones. This prospective cohort study aimed to assess phthalate exposure across the three trimesters of pregnancy and its association with thyroid hormone levels. From 2019 to 2022, we recruited 672 pregnant women, and two urine samples and one blood sample were collected from each participant during the pregnancy. We examined the urine samples from 663, 335, and 294 women in the first, second, and third trimester, respectively, for the following seven phthalate metabolites: monoethyl phthalate (MEP) from diethyl phthalate (DEP); mono-n-butyl phthalate (MnBP) and mono-iso-butyl phthalate (MiBP) from dibutyl phthalate (DBP); monobenzyl phthalate (MBzP) from butyl benzyl phthalate; and three di(2-ethylhexyl) phthalate (DEHP) metabolites, mono-(2-ethyl-5-hydroxyhexyl) phthalate (MEHHP), mono-(2-ethyl-5-oxohexyl) phthalate (MEOHP), and mono-(2-ethyl-5-carboxypentyl) phthalate (MECPP). Additionally, we examined the levels of free thyroxine (FT4), thyroid-stimulating hormone (TSH), and total triiodothyronine (TT3) in the serum samples of the following participants: 596, 627, and 576 in the first trimester; 292, 293, and 282 in the second trimester; and 250, 250, and 248 in the third trimester, respectively. Other than MBzP, which was detected in 25%-33% of the samples, other metabolites were detectable in >86% of urine samples, indicating widespread exposure to DEP, DBP, and DEHP. The detected phthalate exposure levels in our cohort were significantly higher than those reported in other countries. Metabolite levels varied across the trimesters, implying changes in exposure and metabolism throughout pregnancy. The observed variability in urinary concentrations of phthalate metabolites, which ranged from poor to moderate, underscores the importance of taking multiple measurements during pregnancy for precise exposure assessment. Using a linear mixed model, we analyzed the effects of repeated phthalate exposure on thyroid hormone levels while adjusting for potential confounders. We observed significant linear trends in FT4, TSH, and, to a lesser extent, TT3 across quartiles of specific phthalate metabolites. Comparing the highest to the lowest quartiles, we found a significant increase in FT4 levels, ranging from 2 to 3.7%, associated with MEP; MECPP; MEHHP; and the sum of seven metabolites (∑7PAE), three DEHP metabolites (∑3DEHP), two DBP metabolites (∑DBP), and both low molecular weight (∑LMW) and high molecular weight metabolites. Increased TSH levels (5%-16%) were observed for all phthalate metabolites (except MEHHP) and their molar sums, including ∑7PAE. For TT3, a significant increase was observed with MEP (2.2%) and a decrease was observed with ∑DBP (-2.7%). A higher TSH/FT4 ratio was observed with the highest quartiles (third or fourth) of several phthalate metabolites: MEP (8.8%), MiBP (8.7%), MnBP (22.2%), ∑7PAE (15.3%), ∑DBP (16.4%), and ∑LMW (18.6%). These hormonal alterations, most notably in the second and third trimesters, suggest that phthalate exposure may impact fetal growth and development by affecting maternal thyroid function.

Associations between exposure to phthalates and liver function among women undergoing assisted reproductive technology

Phthalates can induce hepatotoxicity in animal studies. We aimed to assess the associations of individual and mixture of urinary phthalate metabolites with serum liver function indicators among 764 women undergoing assisted reproductive technology (ART). In linear models, we observed inverse correlations between urinary mono-benzyl phthalate and serum total protein (TP) as well as globulin (β=-0.27 and -0.23, respectively, P<0.05). Additionally, negative associations were identified between mono-isobutyl phthalate and mono-butyl phthalate (MBP) and aspartate aminotransferase-to-alanine transaminase ratio (AST/ALT) (P<0.05). MBP and the sum of all phthalate metabolites (∑all.phth.m) were positively associated with bilirubin, with β ranging from 0.14 to 0.47. Most phthalate metabolites were also positively related to gamma-glutamyl transferase (GGT) (all P<0.05). In Bayesian kernel machine regression models, phthalate mixture was positively associated with bilirubin and GGT, whereas inversely associated with AST/ALT and TP. Our results suggest that phthalate exposure may impair liver function among women undergoing ART.

Gestational thyroid hormones and autism-related traits in the EARLI and HOME studies

Thyroid hormones are essential for neurodevelopment. Few studies have considered associations with quantitatively measured autism spectrum disorder (ASD)-related traits, which may help elucidate associations for a broader population. Participants were drawn from two prospective pregnancy cohorts: the Early Autism Risk Longitudinal Investigation (EARLI), enrolling pregnant women who already had a child with ASD, and the Health Outcomes and Measures of the Environment (HOME) Study, following pregnant women from the greater Cincinnati, OH area. Gestational thyroid-stimulating hormone (TSH) and free thyroxine (FT4) were measured in mid-pregnancy 16 (±3) weeks gestation serum samples. ASD-related traits were measured using the Social Responsiveness Scale (SRS) at ages 3-8 years. The association was examined using quantile regression, adjusting for maternal and sociodemographic factors. 278 participants (132 from EARLI, 146 from HOME) were included. TSH distributions were similar across cohorts, while FT4 levels were higher in EARLI compared to HOME. In pooled analyses, particularly for those in the highest SRS quantile (95th percentile), higher FT4 levels were associated with increasing SRS scores (β = 5.21, 95% CI = 0.93, 9.48), and higher TSH levels were associated with decreasing SRS scores (β = -6.94, 95% CI = -11.04, -2.83). The association between TSH and SRS remained significant in HOME for the 95% percentile of SRS scores (β = -6.48, 95% CI = -12.16, -0.80), but not EARLI. Results for FT4 were attenuated when examined in the individual cohorts. Our results add to evidence that gestational thyroid hormones may be associated with ASD-related outcomes by suggesting that relationships may differ across the distribution of ASD-related traits and by familial likelihood of ASD.

Prenatal phthalate exposure and sex steroid hormones in newborns: Taiwan Maternal and Infant Cohort Study

BACKGROUND

Newborn anogenital distance (AGD) has been associated with prenatal exposure of phthalates. The association between prenatal phthalate exposure and sex steroid hormones in newborns is unclear.

OBJECT

This study aimed to examine whether cord-blood sex hormone levels were associated with prenatal phthalate exposure and newborn anogenital distance (AGD).

METHODS

In the Taiwan Maternal and Infant Cohort Study, we recruited 1,676 pregnant women in their third trimester in 2012-2015 in Taiwan. We determined 11 urinary phthalate metabolites in pregnant women, three maternal and five cord-blood steroid sex-hormone concentrations. Five hundred and sixty-five mother-infant pairs with sufficient data were included. Trained neonatologists measured 263 newborns' AGD. We examined the associations of prenatal phthalate metabolite levels with AGD and hormones using linear regression models and evaluated correlations between maternal and cord-blood sex hormone levels and AGD.

RESULTS

Compared with the male newborns exposed to maternal phthalate metabolites at the first tertile, AGD was -3.75, -3.43, and -3.53 mm shorter among those exposed at the median tertile of di-2-ethylhexyl phthalate (DEHP) metabolites, monobenzyl phthalate (MBzP), and monomethyl phthalate (MMP), respectively. Compared with those who had exposed at the first tertile, cord-blood follicle-stimulating hormone (FSH) decreased among male newborns exposed at higher levels of MMP, mono-n-butyl phthalate (MnBP), MBzP and DEHP, and among female newborns exposed at higher levels of MMP, MBzP and mono(2-ethyl-5-hydroxyhexyl) phthalate. However, we did not observe significant correlations of maternal or cord-blood sex steroid hormones with newborns' AGDs.

CONCLUSIONS

Alterations in cord-blood sex steroid hormone levels were associated with prenatal phthalate exposures, particularly in male newborns. Women aspiring to be pregnant should be alerted of the need of reducing phthalate exposure.

Phthalate metabolites in urine and follicular fluid in relation to menstrual cycle characteristics in women seeking fertility assistance

BACKGROUND

Phthalates have been shown to disrupt the estrous cycle in animal studies. However, epidemiological research investigating their associations with menstrual cycle characteristics is limited.

OBJECTIVE

To explore the relationships between phthalate exposure and menstrual cycle characteristics among women seeking fertility assistance.

METHODS

We determined the levels of eight phthalate metabolites in both follicular fluid (FF) and urine specimens collected from 441 women in the Tongji Reproductive and Environmental (TREE) cohort, using high-performance liquid chromatography and tandem mass spectrometry. Information about menstrual cycle parameters was obtained through a questionnaire. The impacts of individual and joint exposure to phthalates on menstrual cycle characteristics were assessed using multivariable linear regression, Poisson regression, and quantile g-computation approaches.

RESULTS

After adjusting for relevant covariates, we found that per log10-unit increase in mono(2-ethylhexyl) phthalate (MEHP) level in urine specimens was associated with a decrease of 0.20 days (95 % CI: -0.37, -0.03) in bleeding duration. We also observed that mono(2-ethyl-5-carboxypentyl) phthalate (MECPP) and the sum of di(2-ethylhexyl) phthalate (DEHP) metabolites (∑DEHP) concentrations in FF samples were inversely related to cycle length [β = -1.92 (95 % CI: -3.10, -0.75) and -1.87 (95 % CI: -3.56, -0.19), respectively]. However, we generally observed null associations between phthalate metabolites and irregular cycle, dysmenorrhea, hypomenorrhea, or cycle length variation. Furthermore, we also found that phthalate metabolite mixtures in FF and urine were generally unrelated to menstrual cycle characteristics.

CONCLUSION

Our findings suggest that some DEHP metabolites in FF and urine are inversely associated with menstrual cycle length and menstrual bleeding duration in women attending a fertility center.

Association of exposure to perfluoroalkyl substances (PFAS) and phthalates with thyroid hormones in adolescents from HBM4EU aligned studies

BACKGROUND

Perfluoroalkyl substances (PFAS) and phthalates are synthetic chemicals widely used in various types of consumer products. There is epidemiological and experimental evidence that PFAS and phthalates may alter thyroid hormone levels; however, studies in children and adolescents are limited.

AIM

To investigate the association of exposure to PFAS and phthalate with serum levels of thyroid hormones in European adolescents.

METHODS

A cross-sectional study was conducted in 406 female and 327 male adolescents (14-17 years) from Belgium, Slovakia, and Spain participating in the Aligned Studies of the HBM4EU Project (FLEHS IV, PCB cohort, and BEA, respectively). Concentrations of perfluorooctanoic acid (PFOA), perfluorooctane sulfonate (PFOS), perfluorononanoic acid (PFNA), free thyroxine (FT4), free triiodothyronine (FT3), and thyroid-stimulating hormone (TSH) were measured in sera from study participants, and urinary metabolites of six phthalates (DEP, DiBP, DnBP, BBzP, DEHP, and DiNP) and the non-phthalate plasticizer DINCH® were quantified in spot urine samples. Associations were assessed with linear regression and g-computational models for mixtures. Effect modification by sex was examined.

RESULTS

In females, serum PFOA and the PFAS mixture concentrations were associated with lower FT4 and higher FT3 levels; MEP and the sums of DEHP, DiNP, and DINCH® metabolites (∑DEHP, ∑DiNP, and ∑DINCH) were associated with higher FT4; ∑DEHP with lower FT3; and the phthalate/DINCH® metabolite mixture with higher FT4 and lower FT3. In males, PFOA was associated with lower FT4 and the PFAS mixture with higher TSH levels and lower FT4/TSH ratio; MEP and ∑DiNP were associated with higher FT4; and MBzP, ∑DEHP, and the phthalate/DINCH® metabolite mixture with lower TSH and higher FT4/TSH. PFOA, mono-(2-ethyl-5-hydroxyhexyl) phthalate (OH-MEHP), mono-(2-ethyl-5-oxohexyl) phthalate (oxo-MEHP), and monocarboxyoctyl phthalate (MCOP) made the greatest contribution to the mixture effect.

CONCLUSIONS

Results suggest that exposure to PFAS and phthalates is associated with sex-specific differences in thyroid hormone levels in adolescents.

Sex-specific interactive effect of melamine and DEHP on a marker of early kidney damage in Taiwanese adults: A national population-based study from the Taiwan Biobank

Taiwan had the high incidence of chronic kidney disease (CKD) worldwide. Our objective was to examine associations between daily exposure of phthalates and melamine, two common nephrotoxins, and kidney damage risk in a well-established nationwide cohort. Study subjects were from Taiwan Biobank (TWB) with existing data of questionnaire and biochemical examinations. Average daily intake (ADI) levels of melamine and seven parental phthalates, including DEHP (di-2-ethylhexylphthalate), DiBP (Dibutyl phthalate), DnBP (Di-n-butyl phthalate), BBzP (Butyl benzyl phthalate), DEP (Diethyl phthalate), and DMP (Dimethyl phthalate) were estimated using a creatinine excretion-based model from urine melamine and 10 phthalate metabolites. Urine microalbumin to creatinine ratio (ACR) was used to represent for the outcome of kidney damage. Two statistical strategies were used: First, a weighted quantile sum (WQS) regression model to select the most important exposure variables of ADI levels of phthalates and melamine associated with ACR; Second, to examine effects of those most important exposure variables on ACR in multivariable linear regression models. In total, 1153 eligible adults were left for analyses. Of them, 591 (51.3%) and 562 (48.7%) were men and women, respectively, with a median age of 49 years old. By WQS, a significant and positive association was found between ADI of melamine and phthalates and ACR (β = 0.14, p = 0.002). ADI levels of melamine had the highest weight (0.57), followed by DEHP (0.13). Next, examining the two most important exposures in association with ACR, we found that the higher the melamine and DEHP intakes, the higher the ACR levels were found. An interaction effect was also found between melamine and DEHP intakes on urine ACR (p = 0.015). This result was more prominent in men (p = 0.008) than in women (p = 0.651). Environmental co-exposure of melamine and DEHP can potentially affect ACR in the community-dwelling Taiwanese adult population.

Maternal di-(2-ethylhexyl) phthalate exposure elicits offspring IFN-λ upregulation: Insights from birth cohort, murine model, and in vitro mechanistic analysis

Maternal exposure to di-(2-ethylhexyl)-phthalate (DEHP), an environmental endocrine disruptor, may lead to developmental immunotoxicity in offspring. The causal relationship and underlying mechanism require further study. A subset of Taiwan Maternal and Infant Cohort Study data (n = 283) was analyzed and found a significant association between urinary DEHP metabolite levels from the third trimester of pregnancy and plasma levels of IL-28A and IL-29, named IFNλs, in cord blood. A trans-maternal murine model mimicking human DEHP exposure way showed that bone marrow-derived dendritic cells from maternal DEHP-exposed F1 offspring secreted higher IL-28A levels than control cells, indicating a potential causal relationship. Human bronchial epithelial cell lines treated with DEHP or its primary metabolite, mono-(2-ethyl-5-hexyl) phthalate (MEHP), expressed significantly higher levels of IFNλs mRNA or protein than controls. MEHP's effect on IFNλs expression was blocked by peroxisome proliferator-activated receptor α (PPARα) and PPARγ antagonists, and inhibited by a histone acetyltransferase inhibitor or a histone methyltransferase inhibitor. Chromatin immunoprecipitation assay showed that MEHP treatment promoted histone modifications at H3 and H4 proteins at the promoter regions of Il28a and Il29 genes. These results suggest maternal DEHP exposure could result in high IFNλ expression in offspring, and the health risk of early-life exposure requires further investigation.

Di(2-ethylhexyl) phthalate mediates IL-33 production via aryl hydrocarbon receptor and is associated with childhood allergy development

Background

Few studies assess cord blood biomarkers to predict prenatal exposure to di(2-ethylhexyl) phthalate (DEHP) on the development of allergic diseases later in childhood. IL-33 has been indicated to play an important role in allergic diseases. We evaluated the association of prenatal DEHP exposure and IL-33 in cord blood on the development of allergic diseases. We also investigated the mechanism of DEHP in human lung epithelial cells and asthma animal models.

Methods

66 pregnant women were recruited, and their children followed when they were aged 3 years. Maternal urinary DEHP metabolites were determined using liquid chromatography-electrospray-ionization-tandem mass spectrometry. The effect of DEHP on IL-33 production was investigated in human lung epithelial cells and club cell-specific aryl hydrocarbon receptor (AhR) deficiency mice. ELISA and RT-PCR, respectively, measured the IL-33 cytokine concentration and mRNA expression.

Results

The concentrations of maternal urinary DEHP metabolites and serum IL-33 in cord blood with childhood allergy were significantly higher than those in the non-childhood allergy group. DEHP and MEHP could induce IL-33 production and reverse by AhR antagonist and flavonoids in vitro. Enhanced ovalbumin-induced IL-4 and IL-33 production in bronchoalveolar lavage fluid (BALF) by DEHP exposure and suppressed in club cell-specific AhR null mice. Kaempferol has significantly reversed the DEHP effect in the asthma animal model.

Conclusions

Cord blood IL-33 level was correlated to childhood allergy and associated with maternal DEHP exposure. IL-33 might be a potential target to assess the development of DEHP-related childhood allergic disease. Flavonoids might be the natural antidotes for DEHP.

Exposure to a mixture of non-persistent environmental chemicals and neonatal thyroid function in a cohort with improved exposure assessment

BACKGROUND

In vitro and toxicological studies have shown that non-persistent environmental chemicals can perturb thyroid hormone homeostasis. Epidemiological studies with improved exposure assessment (i.e., repeated urine samples) are needed to evaluate effects of these compounds, individually or as a mixture, in humans. We studied the associations between prenatal exposure to non-persistent environmental chemicals and neonatal thyroid hormones.

METHODS

The study population consisted of 442 mother-child pairs from the French SEPAGES mother-child cohort recruited between July 2014 and July 2017. For each participant, four parabens, five bisphenols, triclosan, triclocarban, benzophenone-3 as well as metabolites of phthalates and of di(isononyl)cyclohexane-1,2-dicarboxylate were assessed in two pools of repeated urine samples (median: 21 spot urines per pool), collected in the 2nd and 3rd trimesters of pregnancy, respectively. Thyroid stimulating hormone (TSH) and total thyroxine (T4) levels were determined in newborns from a heel-prick blood spot. Maternal iodine and selenium were assessed in urine and serum, respectively. Adjusted linear regression (uni-pollutant model) and Bayesian Kernel Machine Regression (BKMR, mixture model) were applied to study overall and sex-stratified associations between chemicals and hormone concentrations.

RESULTS

Interaction with child sex was detected for several compounds. Triclosan, three parabens, and one phthalate metabolite (OH-MPHP) were negatively associated with T4 among girls in the uni-pollutant model. BKMR also suggested a negative association between the mixture and T4 in girls, whereas in boys the association was positive. The mixture was not linked to TSH levels, and for this hormone the uni-pollutant model revealed associations with only a few compounds.

CONCLUSION

Our study, based on repeated urine samples to assess exposure, showed that prenatal exposure to some phenols and phthalates disturb thyroid hormone homeostasis at birth. Furthermore, both uni-pollutant and mixture models, suggested effect modification by child sex, while, to date underlying mechanisms for such sex-differences are not well understood.

Associations between maternal phthalate exposure and neonatal neurobehaviors: The Taiwan maternal and infant cohort study (TMICS)

Previous studies have shown associations between prenatal phthalate exposure and neurobehavioral changes in children. However, few studies have focused on neonatal neurobehavioral development. This study aimed to examine the associations between prenatal phthalate exposure and neonatal neurobehavioral development in the early days of life after birth. This cohort study included 283 mother-infant pairs who participated in the Taiwan Mother Infant Cohort Study during 2012-2015. Each mother was interviewed, and urine samples were collected during the third trimester of pregnancy (weeks 29-40). Eleven common phthalate metabolites in maternal urine were analyzed. The Chinese version of the Neonatal Neurobehavioral Examination was used to evaluate early infant neurobehavioral development within five days of birth. We performed multiple linear regressions to explore the associations between phthalate exposure and neonatal neurobehavioral development. Sex differences in the association between phthalate metabolites and neonatal neurobehaviors were noted. Among girls, tertiles of phthalate metabolite concentrations were associated with worse behavioral responses and tone and motor patterns in the high-molecular-weight phthalate (HMW) and low-molecular-weight phthalate (LMW) groups. Girls in the highest tertile of di-2-ethylhexyl phthalate (DEHP) and mono-isobutyl phthalate (MiBP) had a negative association with tone and motor patterns. Girls in the highest tertile of mono-n-butyl phthalate (MnBP) and MiBP showed a negative association with behavioral responses. In contrast, tertiles of phthalate metabolite exposure were associated with improved neurobehaviors in mono-methyl phthalate (MMP) among boys. The highest tertile of MMP was positively associated with behavioral responses, primitive reflexes, and tone and motor patterns. Our findings suggest that maternal phthalate exposure affects neonatal neurobehavioral development in a sex-specific manner. Despite the relatively small sample size, our findings add to the existing research linking maternal phthalate exposure to neonatal neurobehavioral development. Additional research is needed to determine the potential long-term effects of prenatal phthalate exposure on children.

Di(2-ethylhexyl) phthalate induced thyroid toxicity via endoplasmic reticulum stress: In vivo and in vitro study

Di(2-ethylhexyl) phthalate (DEHP) could induce thyroid injury but the mechanism was unclear. This study combined in vivo and in vitro experiments to clarify the mechanism. In vivo, the offspring of Sprague Dawley rats were gavaged with different doses of DEHP (5, 50, and 250 mg/[kg⋅d]) from in utero to 12 weeks-old. Transcriptome sequencing was used to detect the mRNA expression profile of the offspring's thyroids. Differentially expressed genes were identified, followed by Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis. In vitro, Nthy-ori 3-1 cells were exposed to DEHP's metabolite mono (2-ethylhexyl) phthalate (MEHP) to verify the pathway we found by KEGG analysis. The results indicated that DEHP could disorder the thyroid hormones. Compared with the offspring in control group, the mRNA levels of 656 genes were upregulated in the offspring exposed to 50 mg/(kg⋅d) DEHP. The upregulated genes were enriched in the pathway of "protein processing in the endoplasmic reticulum (ER)." It indicated that the ER stress might play significant role in the thyroid toxicity induced by DEHP. In vitro, the mitochondrial membrane potential (ΔΨm) level of cells was decreased while the reactive oxygen species level was increased after MEHP exposure. MEHP increased the intracellular Ca²⁺ level and induced ER stress. After ER stress was inhibited by the 4-phenylbutyric acid, the thyroid toxicity caused by MEHP was alleviated. Taken together, our results indicated that DEHP could induce thyroid toxicity by activating ER stress.

Associations between phthalate exposure and thyroid function in pregnant women during the first trimester

Phthalates are a class of environmental endocrine disruptors. Previous studies have demonstrated that phthalate exposure can affect thyroid function; however, limited studies have assessed the associations between phthalate exposure and thyroid function, especially thyroid autoimmunity in pregnant women during the first trimester. We recruited participants from a cohort of pregnant women in Beijing, China, and collected urine samples to measure ten phthalate metabolites, serum samples to measure free thyroxine (FT₄), thyroid-stimulating hormone (TSH), thyroid peroxidase antibody (TPOAb) during the first trimester. We included 325 pregnant women without thyroid diseases or dysfunction in this study. Associations between phthalate metabolites and thyroid function parameters were assessed with the Bayesian kernel machine regression (BKMR) model, multiple linear regression model, and restricted cubic spline. In the BKMR model analysis, compared to the 50th percentile, total urinary phthalate metabolites levels were negatively associated with serum TPOAb levels when phthalate metabolites were at or below the 40th percentile. Stratifying by body mass index, total urinary phthalate metabolites levels were negatively associated with serum TPOAb levels in normal weight women when phthalate metabolites were at or below the 45th percentile. However, total urinary phthalate metabolites levels were positively associated with serum TPOAb levels in underweight women when phthalate metabolites were at or below the 30th percentile. In restricted cubic spline analysis, L-shaped nonlinear associations of mono-(2-ethyl-5-carboxypentyl) phthalate (MECPP), mono-(2-ethyl-5-oxohexyl) phthalate (MEOHP), di-(2-ethylhexyl) phthalate (ΣDEHP), and inverted S-shaped nonlinear association of mono-(2-ethyl-5-hydroxyhexyl) phthalate (MEHHP) with TPOAb were observed. In conclusion, our findings suggest that phthalate exposure may affect thyroid autoimmunity in underweight pregnant women during early pregnancy, and the potential effects of phthalate exposure on thyroid autoimmunity may be nonlinear.

Plasticizers: negative impacts on the thyroid hormone system

This review aims to understand the impacts of plasticizers on the thyroid system of animals and humans. The thyroid gland is one of the earliest endocrine glands that appear during embryogenesis. The thyroid gland synthesizes thyroid hormones (TH), triiodothyronine (T3), and thyroxine (T4) that are important in the regulation of body homeostasis. TH plays critical roles in regulating different physiological functions, including metabolism, cell growth, circadian rhythm, and nervous system development. Alteration in thyroid function can lead to different medical problems. In recent years, thyroid-related medical problems have increased and this could be due to rising environmental pollutants. Plasticizers are one such group of a pollutant that impacts thyroid function. Plasticizers are man-made chemicals used in a wide range of products, such as children's toys, food packaging items, building materials, medical devices, cosmetics, and ink. The increased use of plasticizers has resulted in their detection in the environment, animals, and humans. Studies indicated that plasticizers could alter thyroid function in both animals and humans at different levels. Several studies demonstrated a positive and/or negative correlation between plasticizers and serum T4 and T3 levels. Plasticizers could also change the expression of various TH-related genes and proteins, including thyroid-stimulating hormone (TSH), thyrotropin-releasing hormone (TRH), and transporters. Histological analyses demonstrated thyroid follicular cell hypertrophy and hyperplasia in response to several plasticizers. In conclusion, plasticizers could disrupt TH homeostasis and the mechanisms of toxicity could be diverse.

Phthalate's multiple hormonal effects and their supplementary dietary regulation scheme of health risks for children

Four common phthalic acid esters (PAEs), namely, butylbenzyl phthalate (BBzP), dibutyl phthalate (DBP), di(2-ethylhexyl) phthalate (DEHP), and di-n-octyl phthalate (DNOP) that are known to affect children upon exposure, were selected, and the hormone effects were explored during different supplementary food intakes by using methods such as factorial design experiment, molecular docking, and dynamics simulation techniques. A supplementary diet regulation scheme to prevent health risks of PAEs was constructed to avoid or mitigate the hormonal effects in children exposed to PAEs. Firstly, the MM/PBSA binding energy of PAEs with single hormone receptors and multiple hormone receptor complexes was calculated. In addition, 10 foods were selected as external interference conditions to carry out dynamic simulation, which showed that kiwi fruit and broccoli can effectively alleviate the PAEs' hormone effects. Furthermore, inference of the metabolic process of DEHP found that the supplementary diets could effectively promote the metabolism of PAEs. Finally, based on the mechanism analysis, it was confirmed that the selected supplementary diets could inhibit the binding process. This study aims to explore the role of supplementary diets in regulating various PAEs' hormone effects and thereby provide theoretical support for slowing down hormonal effects in children.

Maternal exposure to bis(2-ethylhexyl) phthalate during the thyroid hormone-dependent stage induces persistent emotional and cognitive impairment in middle-aged offspring mice

Prenatal DEHP exposure can cause offspring neurodevelopmental toxicity, but the persistent effects of such exposure window are unclear. This study aimed to investigate the lasting neurobehavioral impact of DEHP on offspring following early exposure from GD9.5 (fetal neural tube closure) to GD16.5 (fetal thyroxin, TH, synthesis). Data showed maternal exposure to DEHP during the thyroid hormone-dependent stage induced a range of neurobehavioral phenotypic changes in adult and middle-aged mice, including anxiety, depression and cognitive impairment. Significant reductions in free TH, TH transporters, and TH metabolic enzyme deiodinase II (D2) were observed in the fetal brain, whereas D3 was elevated, indicating that TH signaling disruption was caused by in utero exposure. Gene expression analyses suggested the expression levels of the TH receptors Trα1, Trβ1 and their downstream target, brain-derived neurotrophic factor, were significantly attenuated, which may partially explain the mechanisms of neurodevelopmental impairment. This study provides new evidence of the persistent effects of sex-specific neurodevelopmental impairment due to in utero DEHP exposure, possibly through damage to the fetal brain TH signaling systems that causes lifelong brain damage. These results further suggest a profound neurobehavioral toxicity of DEHP that may be programmed during early developmental stage exposure and manifested later in life.

Association of phthalate exposure with thyroid function during pregnancy

BACKGROUND

The extent of thyroid disruptive effects of phthalates during pregnancy remains unclear.

AIM

To investigate the association of maternal urinary phthalates with markers of the thyroid system during early pregnancy.

METHODS

Urinary concentrations of phthalate metabolites and serum concentrations of thyroid stimulating hormone (TSH), free and total thyroxine (FT4 and TT4) and free and total triiodothyronine (FT3 and TT3) were measured in pregnant women in early pregnancy in the Swedish Environmental Longitudinal, Mother and child, Asthma and allergy study (2007-ongoing), a population-based prospective cohort.

RESULTS

In the 1,996 included women, higher di-ethyl-hexyl phthalate (DEHP) metabolites were associated with a lower FT4 (β [SE] for the molar sum: -0.13 [0.06], P = 0.03) and a higher TSH/FT4 ratio (0.003 [0.001], P = 0.03). Higher concentrations of di-iso-nonyl phthalate (DINP) metabolites were associated with a lower TT4 (β [SE] for the molar sum: 0.93 [0.44], P = 0.03) as well as with lower TT4/FT4 and TT4/TT3 ratios. Higher metabolites of both dibutyl and butyl-benzyl phthalate (DBP and BBzP) were associated with lower T4/T3 ratio (free and total) and higher FT4/TT4 and FT3/TT3 ratios. A higher diisononyl cyclohexane dicarboxylate (DINCH) metabolite concentration was associated with a higher TT3.

CONCLUSIONS

These results translate results from experimental studies suggesting that exposure to phthalates may interfere with the thyroid system during pregnancy. This is also true for compounds that have been introduced to replace known disruptive phthalates. Further experimental studies should take into account the human evidence to better investigate the potential underlying mechanisms of thyroid disruption by phthalates.

Pregnancy exposure to common-detect organophosphate esters and phthalates and maternal thyroid function

BACKGROUND

Contemporary human populations are exposed to elevated concentrations of organophosphate esters (OPEs) and phthalates. Some metabolites have been linked with altered thyroid function, however, inconsistencies exist across thyroid function biomarkers. Research on OPEs is sparse, particularly during pregnancy, when maintaining normal thyroid function is critical to maternal and fetal health. In this paper, we aimed to characterize relationships between OPEs and phthalates exposure and maternal thyroid function during pregnancy, using a cross-sectional investigation of pregnant women nested within the Norwegian Mother, Father, and Child Cohort (MoBa).

METHODS

We included 473 pregnant women, who were euthyroid and provided bio-samples at 17 weeks' gestation (2004-2008). Four OPE and six phthalate metabolites were measured from urine; six thyroid function biomarkers were estimated from blood. Relationships between thyroid function biomarkers and log-transformed concentrations of OPE and phthalate metabolites were characterized using two approaches that both accounted for confounding by co-exposures: co-pollutant adjusted general linear model (GLM) and Bayesian Kernal Machine Regression (BKMR).

RESULTS

We restricted our analysis to common-detect OPE and phthalate metabolites (>94%): diphenyl phosphate (DPHP), di-n-butyl phosphate (DNBP), and all phthalate metabolites. In GLM, pregnant women with summed di-isononyl phthalate metabolites (∑DiNP) concentrations in the 75th percentile had a 0.37 ng/μg lower total triiodothyronine (TT3): total thyroxine (TT4) ratio (95% credible interval: [-0.59, -0.15]) as compared to those in the 25th percentile, possibly due to small but diverging influences on TT3 (-1.99 ng/dL [-4.52, 0.53]) and TT4 (0.13 μg/dL [-0.01, 0.26]). Similar trends were observed for DNBP and inverse associations were observed for DPHP, monoethyl phthalate, mono-isobutyl phthalate, and mono-n-butyl phthalate. Most associations observed in co-pollutants adjusted GLMs were attenuated towards the null in BKMR, except for the case of ∑DiNP and TT3:TT4 ratio (-0.48 [-0.96, 0.003]).

CONCLUSIONS

Maternal thyroid function varied modestly with ∑DiNP, whereas results for DPHP varied by the type of statistical models.

A critical review on human internal exposure of phthalate metabolites and the associated health risks

Phthalates (PAEs) are popular synthetic chemicals used as plasticizers and solvents for various products, such as polyvinyl chloride or personal care products. Human exposure to PAEs is associated with various diseases, resulting in PAE biomonitoring in humans. Inhalation, dietary ingestion, and dermal absorption are the major human exposure routes. However, estimating the actual exposure dose of PAEs via an external route is difficult. As a result, estimation by internal exposure has become the popular analytical methods to determine the concentrations of phthalate metabolites (mPAEs) in human matrices (such as urine, serum, breast milk, hair, and nails). The various exposure sources and patterns result in different composition profiles of PAEs in biomatrices, which vary from country to country. Nevertheless, the mPAEs of diethyl phthalate (DEP), di-n-butyl phthalate (DnBP), di-iso-butyl phthalate (DiBP), and di-(2-ethylhexyl) phthalate (DEHP) are predominant in the urine. These mPAEs have greater potential health risks for humans. Children have been observed to exhibit higher exposure risks to several mPAEs than adults. Besides age, other influencing factors for phthalate exposure are gender, jobs, and residential areas. Although many studies have reported biological monitoring of PAEs, only a few reviews that adequately summarized the reports are available. The current review appraised available studies on mPAE quantitation in human biomatrices and estimated the dose and health risks of phthalate exposure. While some countries lack biomonitoring data, some countries' data do not reflect the current PAE exposure. Thence, future studies should involve frequent PAE biomonitoring to accurately estimate human exposure to PAEs, which will contribute to health risk assessments of human exposure to PAEs. Such would aid the formulation of corresponding regulations and restrictions by the government.

Prenatal Exposure to Di-Ethyl Phthalate (DEP) Is Related to Increasing Neonatal IgE Levels and the Altering of the Immune Polarization of Helper-T Cells

Introduction: Phthalates are substances that are added to plastic products to increase their plasticity. These substances are released easily into the environment and can act as endocrine disruptors. Epidemiological studies in children have showed inconsistent findings regarding the relationship between prenatal or postnatal exposure to phthalates and the risk of allergic disease. Our hypothesis is that prenatal exposure to phthalates may contribute to the development of allergies in children. Material and methods: The objective of this study was to determine the associations between urinary phthalate metabolite concentrations in pregnant women, maternal atopic diathesis, maternal lifestyle, and cord blood IgE. Pregnant mothers and paired newborns (n = 101) were enrolled from an antenatal clinic. The epidemiologic data and the clinical information were collected using standard questionnaires and medical records. The maternal blood and urine samples were collected at 24–28 weeks gestation, and cord blood IgE, IL-12p70, IL-4, and IL-10 levels were determined from the newborns at birth. The link between phthalates and maternal IgE was also assessed. To investigate the effects of phthalates on neonatal immunity, cord blood mononuclear cells (MNCs) were used for cytokine induction in another in vitro experiment. Results: We found that maternal urine monoethyl phthalate (MEP) (a metabolite of di-ethyl phthalate (DEP)) concentrations are positively correlated with the cord blood IgE of the corresponding newborns. The cord blood IL-12p70 levels of mothers with higher maternal urine MEP groups (high DEP exposure) were lower than mothers with low DEP exposure. In vitro experiments demonstrated that DEP could enhance IL-4 production of cord blood MNCs rather than adult MNCs. Conclusion: Prenatal DEP exposure is related to neonatal IgE level and alternation of cytokines relevant to Th1/Th2 polarization. This suggests the existence of a link between prenatal exposure to specific plasticizers and the future development of allergies.

Association between two common environmental toxicants (phthalates and melamine) and urinary markers of renal injury in the third trimester of pregnant women: The Taiwan Maternal and Infant Cohort Study (TMICS)

BACKGROUND

Exposure to either melamine or phthalate, two common toxicants, during pregnancy may cause adverse health effects, including kidney damage.

OBJECTIVES

We investigated the independent and interactive effect of exposure to melamine and phthalates, particularly di-(2-ethylhexyl) phthalate (DEHP), on markers of early renal injury in women their third trimester of pregnancy in one nationwide birth cohort, the Taiwan Maternal and Infant Cohort Study (TMICS).

METHODS

Between October, 2012 and May, 2015, participants were administered questionnaires, physical examinations, and blood and urine tests during their third trimester. One-spot overnight urine specimens were used to simultaneously measure melamine, 11 phthalate metabolites, and two markers of renal injury, microalbumin and N-acetyl-beta-D-glucosaminidas (NAG). Estimated daily DEHP intake was calculated based on measurement of three urinary DEHP metabolites. Microalbuminuria was defined as having a urinary albumin/creatinine ratio (ACR) higher than 3.5 mg/mmol.

RESULTS

Total 1433 pregnant women were analyzed. The median value for urinary melamine was 0.63 μg/mmol Cr and estimated DEHP intake was 1.84 μg/kg/day. We found subjects in the highest quartile of estimated DEHP intake to have significantly higher urinary ACR (β = 0.095, p = 0.043) and the prevalence of microalbuminuria (adjusted OR = 1.752, 95% confidence interval = 1.118-2.746), compared to those in the lowest quartile. In addition, there was a significant interactive effect between urinary melamine and estimated DEHP intake on urinary ACR and NAG.

CONCLUSION

Our results suggest these two ubiquitous chemicals together may be associated with markers of early kidney injury in pregnant women.

Prenatal Phthalates Exposure and Cord Thyroid Hormones: A Birth Cohort Study in Southern Taiwan

BACKGROUND

The regulation of thyroid hormones in the early stages of gestation plays a crucial role in the outcome of a pregnancy. Furthermore, thyroid hormones are fundamental for the fetal development of all organs, including endocrine hormone changes in uterus. Endocrine disrupting chemicals have been shown to have an effect on thyroid hormone homeostasis in newborns, which affects their later development. Few studies have proposed how phthalates could alter thyroid function through several mechanisms and the possible effects on thyroid hormone homeostasis of phthalates on pregnant women. However, the effects of cord blood phthalates and prenatal phthalate exposure on thyroid hormones in newborns remain unclear.

OBJECTIVES

We aim to follow up on our previous established subjects and determine the correlation between phthalate exposure and thyroid hormones in pregnant women and newborns.

MATERIALS AND METHODS

We recruited 61 pregnant women from the Obstetrics and Gynecology Department of a medical hospital in southern Taiwan and followed up. High performance liquid chromatography electrospray ionization tandem mass spectrometry (HPLC-ESI-MS/MS) was used to analyze urine samples for five phthalate metabolites. Serum levels of thyroid hormones were analyzed using electrochemoluminescence immunoassay (ECLIA) method. We used Spearman and Pearson correlation coefficients to evaluate the correlation between each phthalate metabolites in serum and the thyroid hormone levels in fetus and parturient. Finally, multiple logistic regression was used to explore the relationship between hormones and their corresponding phthalate metabolites in cord blood.

RESULTS

High MBP in cord blood was correlated with negative cord serum TSH in newborns (r = -0.25, p < 0.06). By using multiple linear regression after adjusting for potential confounders (gestational and maternal age), cord serum MBP levels showed a negative association with cord serum TSH (β = 0.217, p < 0.05), cord serum T₄ (β = 1.71, p < 0.05) and cord serum T₄ × TSH (β = 42.8, p < 0.05), respectively.

CONCLUSION

We found that levels of cord serum TSH and T₄ in newborns was significantly negatively associated with cord serum MBP levels after adjusting for significant covariate. The fall in TSH in newborns may potentially be delaying their development.

Maternal Thyroid Disorders and Risk of Autism Spectrum Disorder in Progeny

BACKGROUND

Maternal thyroid dysfunction is suspected of causing adverse neurodevelopmental effects, but current evidence is inconclusive. Epidemiologic investigations generally suggest an association between maternal thyroid dysfunction and neurodevelopment impairments in progeny, but clinical trials of thyroid treatment during pregnancy reported null effects. To better understand these discrepant findings, we evaluated the association between maternal thyroid conditions and autism spectrum disorder (ASD), including examining the role of gestational thyroid-related hormone concentrations and thyroid medications use.

METHODS

Analyses considered 437,222 singleton live births occurring in a large Israeli health fund in 1999-2013, followed through 2016. Thyroid conditions and ASD cases were identified through International Classification of Diseases-9 codes with subsequent validation through review of medical records. Laboratory gestational thyroid hormone measurements were also considered.

RESULTS

Children of mothers who ever experienced hypothyroidism had a higher risk of ASD compared with children of mothers without hypothyroidism (adjusted odds ratio [aOR] = 1.26, 95% confidence interval [CI] = 1.12, 1.42). The association with hyperthyroidism was less consistent, but elevated in main analyses (aOR = 1.42, 95% CI = 1.04, 1.94). These associations were not explained by maternal gestational thyroid hormones levels nor mitigated by gestational use of thyroid medications.

CONCLUSIONS

Results indicate that maternal thyroid conditions are associated with increased ASD risk in progeny, but suggestively not due to direct effects of thyroid hormones. Instead, factors that influence maternal thyroid function could have etiologic roles in ASD through pathways independent of maternal gestational thyroid hormones and thus be unaffected by medication treatment. Factors known to disrupt thyroid function should be examined for possible involvement in ASD etiology.

Urinary phthalate metabolite concentrations, oxidative stress and thyroid function biomarkers among patients with thyroid nodules

Prior human studies have explored effects of phthalate exposures on thyroid function, but the underlying biological mechanisms remain poorly unclear. We aimed to explore the associations between phthalate exposures and thyroid function among a potentially susceptible population such as patients with thyroid nodules, and further to assess the mediating role of oxidative stress. We measured eight phthalate metabolites, three oxidative stress biomarkers [8-hydroxy-2-deoxyguanosine (8-OHdG), 8-iso-prostaglandin F_2α (8-isoPGF_2α) and 4-hydroxy-2-nonenal-mercapturic acid (HNE-MA)] in urine and three thyroid function biomarkers [thyroid-stimulating hormone (TSH), free triiodothyronine (FT3) and free thyroxine (FT4)] in serum among 214 patients with thyroid nodules. Multivariate regression models were applied to assess the associations among urinary phthalate metabolites, oxidative stress and thyroid function biomarkers. The potential mediating role of oxidative stress was explored by mediation analysis. We observed that multiple urinary phthalate metabolites were associated with altered FT4 and increased oxidative stress biomarkers (all FDR-adjusted P ≤ 0.05). Meanwhile, we found that 8-isoPGF_2α was negatively associated with FT3/FT4 among patients with benign thyroid nodules (FDR-adjusted P = 0.08). The mediation analysis indicated that 8-isoPGF_2α mediated the associations of urinary MEHHP and %MEHP with FT3/FT4, with 55.6% and 32.6% proportion of the mediating effects, respectively. Our data suggest that lipid peroxidation may be an intermediate mechanism involved in the effects of certain phthalate exposures on altered thyroid function among patients with benign thyroid nodules.

Environmental Factor-Mediated Transgenerational Inheritance of Igf2r Hypomethylation and Pulmonary Allergic Response via Targeting Dendritic Cells

The developmental origin of allergic diseases has been suggested, but the molecular basis remains enigmatic. Exposure to environmental factors, such as di-(2-ethylhexyl) phthalate (DEHP; a common plasticizer), is suggested to be associated with increased childhood allergic asthma, but the causal relationship and its underlying mechanism remain unknown. This study explored the transgenerational mechanism of DEHP on allergic asthma and dendritic cell (DC) homeostasis through epigenetic modification. In a murine model, ancestral exposure of C57BL/6 mice to low-dose DEHP led to trans-generational promoter hypomethylation of the insulin-like growth factor 2 receptor (Igf2r), concomitant with enhanced Igf2r expression and increased apoptosis prominently in CD8α+ DCs upon ligand stimulation, with consequent reduction in their IL-12 secretion and subsequent T cell-derived IFN-γ, thereby promoting a default Th2-associated pulmonary allergic response. Increased apoptosis was also noted in circulating IGF2Rhigh human DCs. Further, in human placenta, the methylation level at the orthologous IGF2R promoter region was shown to be inversely correlated with the level of maternal DEHP intake. These results support the importance of ancestral phthalate exposure in conferring the trans-generational risk of allergic phenotypes, featuring hypo-methylation of the IGF2R gene and dysregulated DC homeostasis.

Urinary phthalate metabolites are associated with biomarkers of DNA damage and lipid peroxidation in pregnant women - Tainan Birth Cohort Study (TBCS)

Phthalate exposure and oxidative stress have been linked to adverse reproductive outcomes in experimental studies, whereas no clear line has been drawn for human, especially in pregnant women. This study explored relationships between urinary phthalate metabolites and biomarkers of lipid peroxidation and oxidative and nitrosative DNA damage. Measurements from 97 Taiwanese pregnant women were taken at three different times during second and third trimesters. Five oxidative/nitrosative stress biomarkers - 8-hydroxy-2'-deoxyguanosine (8-OHdG), 8-nitroguanine (8-NO₂Gua), 4-hydroxy-2-nonenal-mercapturic acid (HNE-MA), 8-isoprostaglandin F_2α (8-isoPF_2α), and malondialdehyde (MDA), and 11 phthalate metabolites were measured in urine samples. Linear regressions in each visit and linear mixed-model regressions were fitted to estimate percent changes in oxidative/nitrosative stress biomarkers resulting from inter-tertile increase of phthalate metabolite level and the cumulative concentrations of di (2-ethylhexyl) phthalate (DEHP) and dibutyl phthalate. The highest urine concentrations of phthalate metabolites and the greatest number of significant positive associations between phthalate metabolites and oxidative/nitrosative stress biomarkers were observed in the third visit and in repeated measurements analysis, respectively. Of the biomarkers related to DNA damage, 8-OHdG (25.4% inter-tertile increase for mono-iso-butyl phthalate) was more sensitive to phthalate exposure than 8-NO2Gua. Among the biomarkers of lipid peroxidation, HNE-MA (61.2% inter-tertile increase for sum of DEHP metabolites) was more sensitive than 8-isoPF_2α and MDA. Our findings support the hypothesis that pregnant phthalate exposure increases the oxidative stress biomarkers of DNA damage and lipid peroxidation. Future research may elucidate the mediating roles of oxidative/nitrosative stress biomarkers in the link between phthalate exposure and adverse reproductive outcomes.

The Endocrine Disruption of Prenatal Phthalate Exposure in Mother and Offspring

Phthalates are a group of ubiquitous synthetic endocrine-disrupting chemicals. Fetal and neonatal periods are particularly susceptible to endocrine disorders, which prenatal exposure to phthalates causes. There is increasing evidence concerning the potential endocrine disrupting for phthalate exposure during pregnancy. This article aims to review the endocrine impairment and potential outcomes of prenatal phthalate exposure. Prenatal exposure phthalates would disrupt the levels of thyroid, sex hormone, and 25-hydroxyvitamin D in pregnant women or offspring, which results in preterm birth, preeclampsia, maternal glucose disorders, infant cryptorchidism, infant hypospadias, and shorter anogenital distance in newborns, as well as growth restriction not only in infants but also in early adolescence and childhood. The relationship of prenatal phthalate exposure with maternal and neonatal outcomes in human beings was often sex-specific associations. Because of the potentially harmful influence of prenatal phthalate exposure, steps should be taken to prevent or reduce phthalate exposure during pregnancy.

Phthalate and Bisphenol Exposure during Pregnancy and Offspring Nonverbal IQ

BACKGROUND

Prenatal exposures to phthalates and bisphenols are associated with impaired brain development in animals. However, epidemiological studies investigating the association between prenatal phthalate or bisphenol exposure and cognition have produced mixed findings and mostly had modest sample sizes and measured the exposure during the third trimester.

OBJECTIVE

We examined the association between pregnancy maternal urinary biomarkers of phthalate or bisphenol exposure and nonverbal intelligence quotient (IQ) in children 6 years of age.

METHOD

The study sample consisted of 1,282 mother-child pairs participating in the Generation R Study, a population-based birth cohort in Rotterdam, Netherlands (enrollment 2002-2006). We measured maternal urinary concentrations of 18 phthalate metabolites and 8 bisphenols at < 18 , 18-25, and > 25  wks of gestation. Child nonverbal IQ was measured at 6 years of age using the Snijders-Oomen Nonverbal Intelligence Test-Revised. Linear regression models were fit for each of the three collection phases separately, the three collection phases jointly, and for the averaged prenatal exposure across pregnancy.

RESULTS

Higher urinary concentrations of phthalate metabolites during early pregnancy were associated with lower child nonverbal IQ score [e.g., B per 10-fold increase in summed low-molecular weight phthalates = - 1.7 (95% CI: - 3.1 , - 0.3 )]. This association remained unchanged when adjusted for mid and late pregnancy exposures. We also observed an inverse association between late pregnancy di-n-octyl phthalate (DNOP) exposure and nonverbal IQ. Maternal urinary concentrations of bisphenols were not associated with child nonverbal IQ. There was no effect estimate modification by sex.

CONCLUSIONS

We did not observe that maternal biomarkers of bisphenol exposure are associated with nonverbal IQ. We found that phthalate exposure in early pregnancy and DNOP exposure in late pregnancy are associated with lower nonverbal IQ scores in children. Our results might suggest that particularly early pregnancy is a sensitive window of phthalate exposure, but future studies are needed to replicate our findings. https://doi.org/10.1289/EHP6047.

Urinary Concentrations of Phthalate Metabolite Mixtures in Relation to Serum Biomarkers of Thyroid Function and Autoimmunity among Women from a Fertility Center

BACKGROUND

Although previous epidemiological studies have explored associations of phthalate metabolites with thyroid function, no studies to date have assessed associations of mixtures with thyroid function and autoimmunity among potentially susceptible subgroups such as subfertile women.

OBJECTIVE

We aimed to explore associations of mixtures of urinary phthalate metabolites with serum markers of thyroid function and autoimmunity.

METHODS

This cross-sectional study included 558 women attending a fertility center who provided one spot urine and one blood sample at enrollment (2005-2015). We quantified urinary concentrations of eight phthalate metabolites using mass spectrometry, and biomarkers of thyroid function [thyroid-stimulating hormone (TSH), free and total thyroxine (fT4, TT4) and triiodothyronine (fT3, TT3), and autoimmunity [thyroid peroxidase and thyroglobulin antibodies (TPOAb and TgAb, respectively)] in serum using electrochemiluminescence assays. We applied principal component analysis (PCA) and Bayesian kernel machine regression (BKMR) to identify the main patterns of urinary phthalate metabolites. We used linear mixed models to assess the association between PCA-derived factor scores in quintiles and serum thyroid function and autoimmunity, adjusting for age, body mass index (BMI), specific gravity (SG), and, for the PCA, other factor scores.

RESULTS

We observed two factors using PCA, one representing the di(2-ethylhexyl) (DEHP) and another non-DEHP metabolites. Compared to women in the lowest quintile of the DEHP factor scores, women in the highest quintile had significantly lower serum concentrations of fT4, TT4, fT3, and TT3 [absolute difference: -0.62; 95% confidence interval (CI): -0.12, -0.01; p=0.04; absolute difference: -8.31; 95% CI: -13.8, -2.85; p=0.003; absolute difference: -0.37; 95% CI: 0.54, -0.19; p<0.0001; and absolute difference: -0.21; 95% CI: -0.32, -0.10; p=0.003, respectively]. Using BKMR, we observed that mono(2-ethyl-5-hydroxyhexyl) phthalate (MEHHP) was the primary contributor to these negative associations. DEHP and non-DEHP factor scores were not associated with serum TSH, TgAb, or TPOAb.

CONCLUSIONS

Mixtures of urinary DEHP metabolites were inversely associated with serum biomarkers of thyroid function but not with autoimmunity, which were within normal ranges for healthy adult women. https://doi.org/10.1289/EHP6740.

Associations between urine phthalate metabolites and thyroid function in pregnant women and the influence of iodine status

BACKGROUND

Human populations, including susceptible subpopulations such as pregnant women and their fetuses, are continuously exposed to phthalates. Phthalates may affect the thyroid hormone system, causing concern for pregnancy health, birth outcomes and child development. Few studies have investigated the joint effect of phthalates on thyroid function in pregnant women, although they are present as a mixture with highly inter-correlated compounds. Additionally, no studies have investigated if the key nutrient for thyroid health, iodine, modifies these relationships.

METHODS

In this study, we examined the cross-sectional relationships between concentrations of 12 urinary phthalate metabolites and 6 plasma thyroid function biomarkers measured mid-pregnancy (~17 week gestation) in pregnant women (N = 1072), that were selected from a population-based prospective birth cohort, The Norwegian Mother, Father and Child Cohort study (MoBa). We investigated if the phthalate metabolite-thyroid function biomarker associations differed by iodine status by using a validated estimate of habitual dietary iodine intake based on a food frequency questionnaire from the 22nd gestation week. We accounted for the phthalate metabolite mixture by factor analyses, ultimately reducing the exposure into two uncorrelated factors. These factors were used as predictors in multivariable adjusted linear regression models with thyroid function biomarkers as the outcomes.

RESULTS

Factor 1, which included high loadings for mono-iso-butyl phthalate (MiBP), mono-n-butyl phthalate (MnBP), and monobenzyl phthalate (MBzP), was associated with increased total triiodothyronine (TT3) and free T3 index (fT3i). These associations appeared to be driven primarily by women with low iodine intake (<150 µg/day, ~70% of our sample). Iodine intake significantly modified (p-interaction < 0.05) the association of factor 1 with thyroid stimulating hormone (TSH), total thyroxine (TT4) and free T4 index (fT4i), such that only among women in the high iodine intake category (≥150 µg/day, i.e. sufficient) was this factor associated with increased TSH and decreased TT4 and FT4i, respectively. In contrast, factor 2, which included high loadings for di-2-ethylhexyl phthalate metabolites (∑DEHP) and di-iso-nonyl phthalate metabolites (∑DiNP), was associated with a decrease in TT3 and fT3i, which appeared fairly uniform across iodine intake categories.

CONCLUSION

We find that phthalate exposure is associated with thyroid function in mid-pregnancy among Norwegian women, and that iodine intake, which is essential for thyroid health, could influence some of these relationships.

Development of analytical method of melamine in placenta from pregnant women by isotope-dilution liquid chromatography/tandem mass spectrometry

RATIONALE

Melamine is ubiquitously present in our daily life. It has a known effect on the kidneys, but it may also adversely affect the reproduction system. We have developed an analytical method for measuring melamine levels in maternal placenta and correlated these levels with melamine concentrations in urine, a necessary step in finding out if melamine might cross the placenta and enter the circulation of the fetus.

METHODS

We used liquid-liquid extraction, clean up by solid-phase extraction (SPE), and isotope-dilution liquid chromatography/tandem mass spectrometry (LC/MS/MS) to measure melamine in placenta specimens. The results of this method were assessed for linearity, limits of quantitation (LOQs), and intra- and inter-assay precision as well as accuracy, matrix effect, and recovery rate.

RESULTS

Calibration curves indicated good linearity (r >0.995) over concentrations ranging from 5 to 500 ng/mL in placenta specimens, intra- and inter-assay precision from 0.89% to 27.07%, and accuracy from 92.4% to123.5%. Recovery ranged from 63.9 to 83.9%, and the LOQ was 5 ng/mL in placenta (0.2 g). Placental melamine levels ranged from 7.87 to19.64 ng/mL, all detectable (n = 8). Pregnant women with higher levels of urinary melamine had higher placenta melamine levels than those with non-detectable urinary melamine, though the results were not significantly different (p = 0.149, n = 4 in each group).

CONCLUSIONS

The results of this study suggest that pregnant women were exposed to low doses of melamine in their daily lives as measured in urine samples and placenta specimens. It is unclear whether placenta melamine concentrations can better represent long-term exposure than urine or whether melamine in the uterus can enter the fetus via this route.

A strategy to validate a selection of human effect biomarkers using adverse outcome pathways: Proof of concept for phthalates and reproductive effects

Human biomonitoring measures the concentrations of environmental chemicals or their metabolites in body fluids or tissues. Complementing exposure biomarkers with mechanistically based effect biomarkers may further elucidate causal pathways between chemical exposure and adverse health outcomes. We combined information on effect biomarkers previously implemented in human observational studies with mechanisms of action reported in experimental studies and with information from published Adverse Outcome Pathways (AOPs), focusing on adverse reproductive effects of phthalate exposure. Phthalates constitute a group of chemicals that are ubiquitous in consumer products and have been related to a wide range of adverse health effects. As a result of a comprehensive literature search, we present an overview of effect biomarkers for reproductive toxicity that are substantiated by mechanistic information. The activation of several receptors, such as PPARα, PPARγ, and GR, may initiate events leading to impaired male and female fertility as well as other adverse effects of phthalate exposure. Therefore, these receptors appear as promising targets for the development of novel effect biomarkers. The proposed strategy connects the fields of epidemiology and toxicology and may strengthen the weight of evidence in observational studies that link chemical exposures to health outcomes.

Associations of Phthalates and Phthalate Replacements With CRH and Other Hormones Among Pregnant Women in Puerto Rico

CONTEXT

Phthalates are endocrine-disrupting chemicals that may be associated with adverse birth outcomes. Dysregulation of maternal endocrine homeostasis could be a possible biological pathway between phthalates and birth outcomes.

OBJECTIVE

Examine associations between 19 maternal urinary phthalate or phthalate replacement metabolites and 9 serum hormones measured over two time points during pregnancy.

DESIGN

Longitudinal study conducted in the PROTECT pregnancy cohort.

SETTING

Puerto Rico.

PATIENTS

Six hundred seventy-seven women in the first trimester of pregnancy.

MAIN OUTCOME MEASURES SERUM

CRH, estriol, SHBG, progesterone, TSH, total T3, free T4, total T4, and testosterone.

RESULTS

T3 was significantly associated with most metabolites. CRH was inversely associated with mono carboxyisononyl phthalate [MCNP; percent change (%Δ), -4.08; 95% CI, -7.24, -0.804], mono-3-carboxypropyl phthalate (MCPP; %Δ, -5.25; 95% CI, -8.26, -2.14), mono-2-ethyl-5-carboxypentyl phthalate (MECPP; %Δ, -18.4; 95% CI, -30.4, -4.37), mono-2-ethyl-5-hydroxyhexyl phthalate (MEHHP; %Δ, -13.4; 95% CI, -22.7, -2.92), and mono-2-ethyl-5-oxohexyl phthalate (MEOHP; %Δ, -12.7; 95% CI, -22.2, -2.20). Positive associations were found between numerous phthalate metabolites and free T4, T4, and the T3/T4 ratio. Testosterone was positively associated with mono hydroxybutyl phthalate (MHBP; %Δ, 4.71; 95% CI, 0.27, 9.35) and inversely associated with monoethyl phthalate (MEP; %Δ, -14.5; 95% CI, -24.3, -3.42), and relationships with MCNP and mono carboxyisooctyl phthalate (MCOP) were significantly modified by study visit. Finally, an inverse association was found between mono-2-ethyl-5-hydrohexyl terephthalate (MEHHTP), a terephthalate metabolite, and progesterone at visit 3 only (%Δ, -13.1; 95% CI, -22.3, -2.75).

CONCLUSIONS

These results indicate that exposure to phthalates may differentially impact the maternal endocrine system at different points during pregnancy, and that exposures to phthalate replacement chemicals may be particularly important to consider in future human health studies.

The association between prenatal exposure to phthalates and cognition and neurobehavior of children-evidence from birth cohorts

BACKGROUND

Phthalate have been detected widely in the environment; while several studies have indicated that prenatal phthalate exposure has adverse effects on neurodevelopment, the results were inconsistent.

OBJECTIVE

We aimed to determine the current research status of the relationship between prenatal exposure to different types of phthalate and cognition and behavioral development in children. We conducted a systematic review to evaluate the current state of knowledge.

METHODS

We systematically searched PubMed, Web of Science, and EMBASE electronic databases up to May 2018 with manual searches of the references of retrieved publications and relevant reviews. Only birth cohort studies that reported on the association between phthalate exposure and cognitive or behavioral development were included in this review. We evaluated the risk of bias for each of the included studies using a modified instrument based on the Cochrane Collaboration's "Risk of Bias" tool.

RESULT

Twenty-six birth cohort studies met our inclusion criteria, nine of which investigated the impact of phthalate exposure during pregnancy on cognition, 13 on neurobehavior, and 4 on both cognition and neurobehavior. However, ten articles reported that the effect of prenatal exposure to phthalates on cognitive development was statistically significant, 15 articles reported that the effect of prenatal exposure to phthalates on neurobehavior was statistically significant. The effect of prenatal phthalate exposure on neurodevelopment differed according to sex, but the results are inconsistent, for instance, among the five studies investigating the association between mental development index (MDI) and Mono-n-butyl phthalate (MnBP), two of them showed a significantly decreasing MDI scores with increasing concentrations of MnBP among girls, but among boys one study showed the inverse association, another showed the positive association.

CONCLUSION

Di(2-ethylhexyl) phthalate, dibutyl phthalate, butyl-benzyl phthalate and di-ethyl phthalate exposure during pregnancy was associated with lower cognitive scores and worse behavior in offspring, and sex-specific effects on cognitive, psychomotor, and behavioral development were identified, especially the impact of phthalate exposure on neurobehavior in boys.

Association Between Diethylhexyl Phthalate Exposure and Thyroid Function: A Meta-Analysis

BACKGROUND

Diethylhexyl phthalate (DEHP) is widely used in industrial products, particularly as plasticizers and softeners. Because it is used extensively, DEHP has been detected in humans worldwide. Although epidemiological studies suggest that DEHP can disrupt the function of the hypothalamic-pituitary-thyroid (HPT) axis, evidence on the association between DEHP exposure and thyroid function remains inconclusive. Therefore, a comprehensive meta-analysis was performed to investigate the association between DEHP exposure and the HPT axis in humans.

METHODS

A literature search of the MEDLINE, EMBASE, and Web of Science databases was conducted to search for studies in which the correlation coefficient values or regression coefficient values between three major DEHP metabolites (i.e., monoethylhexyl phthalate [MEHP], mono [2-ethyl-5-hydroxyhexyl] phthalate [MEHHP], and mono [2-ethyl-5-oxohexyl] phthalate) and thyrotropin, free thyroxine (T4), or total T4 were determined. The association between DEHPs and thyroid hormone levels were evaluated using Pearson's correlation coefficients.

RESULTS

Thirteen eligible articles were included. Urinary MEHP and MEHHP concentration was negatively correlated with total T4. Pooled correlation coefficients between MEHP/MEHHP and total T4 were -0.02 [confidence interval (CI) -0.05 to 0.00] and -0.03 [CI -0.05 to -0.01], respectively. Urinary mono (2-ethyl-5-oxohexyl) phthalate concentration was positively correlated with thyrotropin, and the pooled correlation coefficient was 0.02 [CI 0.00-0.04].

CONCLUSIONS

The findings of this meta-analysis suggest a significant association between the exposure of DEHP metabolites and the function of the HPT axis.

Personal care products use and phthalate exposure levels among pregnant women

BACKGROUND

Fetuses are susceptible to phthalates, known endocrine disrupting chemicals, within sensitive windows of development. It is crucial to determine the major sources of phthalates to reduce exposure. This study aims to examine the associations between usage patterns of personal care products (PCPs) and urinary levels of phthalate metabolites across pregnancy in a multi-hospital based birth cohort.

METHODS

During 2012-2015, we conducted a birth cohort study named the Taiwan Mother Infant Cohort Study (TMICS). Usage patterns of PCPs were obtained using structured questionnaires during the third trimester of pregnancy. Spot urine samples were collected at each trimester, and levels of eleven phthalate metabolites were measured by liquid chromatography tandem mass spectrometry. The association of PCPs use with urinary phthalate metabolite concentrations was assessed using GEE models.

RESULTS

Among the 1676 pregnant women participated in TMICS, 281 who provided two or three urine samples across pregnancy were included. The levels of several phthalate metabolites were significantly associated with the use of PCPs, particularly leave-on PCPs. With the increasing use of skin toners (11.7%; 95% CI: 1.5%, 22.9%), lipsticks (13.2%; 95% CI: 4.6%, 22.5%), and essential oils (21.8%; 95% CI: 9.1%, 36.0%), individuals are exposed to higher concentrations of mono-ethyl phthalate (MEP). Additionally, a positive trend was found regarding the number of leave-on PCPs used and the measured change in MEP concentrations (P for trend = 0.01). Other positive associations included MBzP and body lotions (7.9%; 95% CI: 0.1%, 16.2%). With regard to rinse-off PCPs, we found a positive association between urinary MBzP and shampoo use, and a negative association between urinary MMP and face wash.

CONCLUSION

Leave-on PCPs were found to be a more probable source of phthalate exposure than the use of rinse-off PCPs. We suggest pregnant women reduce the frequency of leave-on PCPs use during pregnancy to avoid such phthalate exposure.

Analysis of detection results of thyroid function-related indexes in pregnant women and establishment of the reference interval

Detection results of free thyroxine (FT4), thyroid stimulating hormone (TSH) and thyroid peroxidase antibody (TPOAb) in pregnant women in Linyi region were investigated. A total of 22,235 healthy pregnant women admitted to Women and Children's Health Care Hospital of Linyi from October 2016 to October 2017 were selected and divided into the first-trimester, second-trimester and third-trimester pregnancy groups. Non-pregnant women in the same period were selected as the control group. Roche E601 electrochemiluminescence apparatus was applied to detect FT4, TSH and TPOAb, and statistical analysis was then carried out for the detected data. The positive rate in the third trimester of pregnancy was obviously higher than those in the first and second trimesters of pregnancy (P<0.05). With the prolongation of pregnancy, the reference interval of FT4 was gradually decreased, among which the intervals in the second and third trimesters of pregnancy were significantly lower than those in the non-pregnancy (P<0.05). With the prolongation of pregnancy, the interval in the first trimester of pregnancy was markedly smaller than that in the non-pregnancy group. With the increase of age, the levels of FT4 and TSH tended to be reduced, but the TSH level was increased to a certain degree in patients aged over 40 years. There were differences in the FT4 and TSH reference intervals during pregnancy in comparison among different regions and different detection methods. Region-specific reference intervals need to be established for different trimesters of pregnancy and different detection methods, which is conducive to accurate clinical judgment of thyroid function during pregnancy. TPOAb monitoring needs to be strengthened in the third trimester of pregnancy, and attention should be paid to the changes in thyroid function in pregnant women aged over 40 years.

Prenatal exposure to phthalates and autism spectrum disorder in the MARBLES study

BACKGROUND

Evidence from experimental and observational studies suggests that prenatal phthalate exposures may be associated with autism spectrum disorder (ASD). We examined whether prenatal phthalate exposures were associated with an increased risk of ASD.

METHODS

We quantified 14 metabolites of eight phthalates in 636 multiple maternal urine samples collected during 2nd and 3rd trimesters of pregnancy from 201 mother-child pairs in MARBLES (Markers of Autism Risk in Babies - Learning Early Signs), a high-risk ASD longitudinal cohort. At 3 years old, children were clinically assessed for ASD and classified into three diagnostic categories: ASD (n = 46), non-typical development (Non-TD, n = 55), and typical development (TD, n = 100). We used multinomial logistic regression to evaluate the association of phthalate metabolite concentrations with ASD and Non-TD.

RESULTS

Most associations of phthalate biomarkers with both ASD and Non-TD were null, with the exception that monoethyl phthalate (MEP) was significantly associated with an increased risk of Non-TD (per 2.72-fold relative increase in concentration: Relative risk ratio (RRR) = 1.38; 95% confidence interval (CI): 1.01, 1.90). When stratified by prenatal vitamin use during the first month of pregnancy, among mothers who took vitamins, ASD risk was inversely associated with mono-isobutyl phthalate (MiBP, RRR = 0.44; 95% CI: 0.21, 0.88), mono(3-carboxypropyl) phthalate (MCPP, RRR = 0.41; 95% CI: 0.20, 0.83) and mono-carboxyisooctyl phthalate (MCOP, RRR = 0.49; 95% CI: 0.27, 0.88), but among mothers who did not take prenatal vitamins, Non-TD risk was positively associated with MCPP (RRR = 5.09; 95% CI: 2.05, 12.6), MCOP (RRR = 1.86; 95% CI: 1.01, 3.39), and mono-carboxyisononyl phthalate (MCNP, RRR = 3.67; 95% CI: 1.80, 7.48). When stratified by sex, among boys, MEP, monobenzyl phthalate, MCPP, MCNP, and sum of di(2-ethylhexyl) phthalate metabolites (ΣDEHP) were positively associated with Non-TD risk, but associations with ASD were null. Among girls, associations with both ASD and Non-TD were null.

CONCLUSIONS

Our study showed that phthalate exposures in mid- to late pregnancy were not associated with ASD in children from this high-risk ASD cohort. Further studies should be conducted in the general population without high-risk genes to confirm our findings.

Temporal Variability of Cumulative Risk Assessment on Phthalates in Chinese Pregnant Women: Repeated Measurement Analysis

The assessment of the combined effects of multiple phthalate exposures at low levels is a newly developed concept to avoid underestimating their actual cumulative health risk. A previous study included 3455 Chinese pregnant women. Each woman provided up to three urine samples (in total 9529). This previous study characterized the concentrations of phthalate metabolites. In the present study, the data from 9529 samples was reanalyzed to examine the cumulative risk assessment (CRA) with two models: (1) the creatinine-based and (2) the volume-based. Hazard index (HI) values for three phthalates, dibutyl phthalate, butyl benzyl phthalate, and di(2-ethylhexyl) phthalate, in the first, second, and third trimesters of pregnancy, were calculated, respectively. In creatinine-based model, 3.43%, 14.63%, and 17.28% of women showed HI based on the European Food Safety Authority tolerable daily intake exceeding 1 in the first, second, and third trimester of pregnancy, respectively. The intraclass correlation coefficient of HI was 0.49 (95% confidence interval: 0.46-0.53). Spearman correlations between HI of the creatinine model and ∑androgen disruptor (a developed potency weighted approach) ranged from 0.824 to 0.984. In summary, this study suggested a considerable risk of cumulative exposure to phthalates during the whole gestation in Chinese pregnant women. In addition, moderate temporal reproducibility indicated that single HI, estimated by the phthalate concentration in single spot of urine, seemed representative to describe the throughout pregnancy CRA. Finally, strong correlation between HI of the creatinine model and ∑androgen disruptor revealed that the creatinine-based model was more appropriate to evaluate the CRA.

Prenatal Phthalates, Maternal Thyroid Function, and Risk of Attention-Deficit Hyperactivity Disorder in the Norwegian Mother and Child Cohort

BACKGROUND

There is growing concern that phthalate exposures may have an impact on child neurodevelopment. Prenatal exposure to phthalates has been linked with externalizing behaviors and executive functioning defects suggestive of an attention-deficit hyperactivity disorder (ADHD) phenotype.

OBJECTIVES

We undertook an investigation into whether prenatal exposure to phthalates was associated with clinically confirmed ADHD in a population-based nested case-control study of the Norwegian Mother and Child Cohort (MoBa) between the years 2003 and 2008.

METHODS

Phthalate metabolites were measured in maternal urine collected at midpregnancy. Cases of ADHD (n=297) were obtained through linkage between MoBa and the Norwegian National Patient Registry. A random sample of controls (n=553) from the MoBa population was obtained.

RESULTS

In multivariable adjusted coexposure models, the sum of di-2-ethylhexyl phthalate metabolites (∑DEHP) was associated with a monotonically increasing risk of ADHD. Children of mothers in the highest quintile of ∑DEHP had almost three times the odds of an ADHD diagnosis as those in the lowest [OR=2.99 (95% CI: 1.47, 5.49)]. When ∑DEHP was modeled as a log-linear (natural log) term, for each log-unit increase in exposure, the odds of ADHD increased by 47% [OR=1.47 (95% CI: 1.09, 1.94)]. We detected no significant modification by sex or mediation by prenatal maternal thyroid function or by preterm delivery.

CONCLUSIONS

In this population-based case-control study of clinical ADHD, maternal urinary concentrations of DEHP were monotonically associated with increased risk of ADHD. Additional research is needed to evaluate potential mechanisms linking phthalates to ADHD. https://doi.org/10.1289/EHP2358.

Disruption in Thyroid Signaling Pathway: A Mechanism for the Effect of Endocrine-Disrupting Chemicals on Child Neurodevelopment

Thyroid hormones are crucial in normal brain development. Transient and mild thyroid hormone insufficiency in pregnancy is also associated with impaired neurodevelopment in the offspring (e.g., 3-4 IQ score loss in association with maternal free thyroxine in the lowest fifth percentile). While inadequate iodine intake remains the most common underlying cause of mild thyroid hormone insufficiency in vulnerable populations including pregnant women, other factors such as exposure to environmental contaminants have recently attracted increasing attention, in particular in interaction with iodine deficiency. Endocrine-disrupting chemicals (EDCs) are natural and synthetic substances with ubiquitous exposure in children and adults including pregnant women. EDCs interfere, temporarily or permanently, with hormonal signaling pathways in the endocrine system by binding to hormone receptors and modifying gene expression. Other mechanisms involve alterations in production, metabolism, and transfer of hormones. Experimental studies have shown that exposures to EDCs affect various brain processes such as neurogenesis, neural differentiation and migration, as well as neural connectivity. Neuroimaging studies confirm brain morphological abnormalities (e.g., cortical thinning) consistent with neurodevelopmental impairments as a result of EDC exposures at standard use levels. In this review, we provide an overview of present findings from toxicological and human studies on the anti-thyroid effect of EDCs with a specific attention to fetal and early childhood exposure. This brief overview highlights the need for additional multidisciplinary studies with a focus on thyroid disruption as an underlying mechanism for developmental neurotoxicity of EDC, which can provide insight into modifiable risk factors of developmental delays in children.

Longitudinal assessment of prenatal phthalate exposure on serum and cord thyroid hormones homeostasis during pregnancy - Tainan birth cohort study (TBCS)

An increasing number of studies have revealed that phthalate exposure alters thyroid hormone homeostasis in the general population, but there is insufficient evidence of the effect of longitudinal maternal phthalate exposure on maternal and fetal thyroid hormones during pregnancy. We longitudinally assessed the effect of prenatal phthalate exposure in pregnant women on umbilical cord and maternal thyroid hormones at three trimesters during pregnancy. We recruited 98 pregnant women and collected urine and blood samples at three trimesters in an obstetrics clinic in Southern Taiwan from 2013 to 2014. We analyzed the concentrations of 11 urinary phthalate metabolites, including monoethylhexyl phthalate, mono-(2-ethyl-5-oxo-hexyl) phthalate (MEOHP), mono-(2-ethyl-5-hydroxyhexyl) phthalate, mono-(2-ethyl-5-carboxypentyl) phthalate (MECPP), mono-n-butyl phthalate, monoisobutyl phthalate (MiBP), monoethyl phthalate (MEP), using online liquid chromatography-tandem mass spectrometry. The cord and maternal serum levels of thyroxine (T₄), free T₄, triiodothyronine (T₃), thyroid-stimulating hormone (TSH), and thyroxine-binding globulin were measured using an electrochemiluminescence immunoassay. A mixed-model analysis was utilized to assess the effect of longitudinal phthalate exposure on thyroid hormones and adjusted for significant covariates. We found that urinary MiBP (β=-0.065, 95% confidence interval (CI): -0.124, -0.005), and MEOHP (β=-0.083, 95% CI: -0.157, -0.009) were significantly negatively associated with serum TSH. Urinary MECPP was inversely related to serum T₃ (β=-0.027, 95% CI: -0.047, -0.006). Urinary MEP (β=0.014, 95% CI: -0.001, 0.028) and MiBP (β=0.033, 95% CI: 0.018, 0.049) were positively related to free T₄. We found that cord serum T₃ (β=0.067, 95% CI: 0.003, 0.131) and free T₄ (β=0.031, 95% CI: 0.001, 0.062) levels had significant positive associations with maternal ΣDBPm levels at the second trimester. We concluded that different phthalates exposure windows during gestation may alter cord and serum thyroid hormone homoeostasis.

Interaction of melamine and di-(2-ethylhexyl) phthalate exposure on markers of early renal damage in children: The 2011 Taiwan food scandal

Melamine and phthalate, mainly di-(2-ethylhexyl) phthalate (DEHP), are ubiquitously present in the general environment. We investigated whether urine melamine levels can modify the relationship between DEHP exposure and markers of early renal damage in children. A nationwide health survey for Children aged ≤12 years possibly exposed to phthalates were enrolled between August 2012 and January 2013. They were administered questionnaires to collect details regarding past DEHP exposure to phthalate-tainted foodstuffs. Urine samples were measured melamine levels, phthalate metabolites and biomarkers of renal damage, including urine microalbumin/creatinine ratio (ACR), N-acetyl-beta-d-glucosaminidase (NAG), and β2-microglobulin. The study included 224 children who had a median urine melamine level (μg/mmol creatinine) of 1.61 ranging 0.18-47.42. Positive correlations were found between urine melamine levels and urine ACR as well as urine NAG levels (both Spearman correlation coefficients r = 0.24, n = 224, p < .001). The higher the past DEHP exposure or urine melamine levels, the higher the prevalence of microalbuminuria. An interaction effect was also found between urine melamine levels and past DEHP exposure on urine ACR. Melamine levels may further modify the effect of past DEHP exposure on urine ACR in children.

Maternal urinary phthalate metabolites during pregnancy and thyroid hormone concentrations in maternal and cord sera: The HOME Study

BACKGROUND

Phthalates, endocrine-disrupting chemicals that are commonly found in consumer products, may adversely affect thyroid hormones, but findings from prior epidemiologic studies are inconsistent.

OBJECTIVES

In a prospective cohort study, we investigated whether maternal urinary phthalate metabolite concentrations and phthalate mixtures measured during pregnancy were associated with thyroid hormones among pregnant women and newborns.

METHODS

We measured nine phthalate metabolites [monoethyl phthalate (MEP), mono-n-butyl phthalate, mono-isobutyl phthalate, monobenzyl phthalate (MBzP), and four monoesthers of di(2-ethylhexyl) phthalate] in urine collected at approximately 16 and 26 weeks' gestation among women in the Health Outcomes and Measures of the Environment Study (2003-2006, Cincinnati, Ohio). Thyroid stimulating hormone (TSH) and free and total thyroxine and triiodothyronine were measured in maternal serum at 16 weeks' gestation (n = 202) and cord serum at delivery (n = 276). We used multivariable linear regression to assess associations between individual urinary phthalate metabolites and concentrations of maternal or cord serum thyroid hormones. We used weighted quantile sum regression (WQS) to create a phthalate index describing combined concentrations of phthalate metabolites and to investigate associations of the phthalate index with individual thyroid hormones.

RESULTS

With each 10-fold increase in 16-week maternal urinary MEP, maternal serum total thyroxine (TT₄) decreased by 0.52 μg/dL (95% CI: -1.01, -0.03). For each 10-fold increase in average (16- and 26-week) maternal urinary MBzP, cord serum TSH decreased by 19% (95% CI: -33.1, -1.9). Among mothers, the phthalate index was inversely associated with maternal serum TT₄ (WQS beta = -0.60; 95% CI: -1.01, -0.18). Among newborns, the phthalate index was inversely associated with both cord serum TSH (WQS beta = -0.11; 95% CI: -0.20, -0.03) and TT₄ (WQS beta = -0.53; 95% CI: -0.90, -0.16).

CONCLUSION

Our results suggest that co-exposure to multiple phthalates was inversely associated with certain thyroid hormones (TT₄ in pregnant women and newborns, and TSH in newborns) in this birth cohort. These findings highlight the need to study chemical mixtures in environmental epidemiology.

Evidence of high di(2-ethylhexyl) phthalate (DEHP) exposure due to tainted food intake in Taiwanese pregnant women and the health effects on birth outcomes

The contamination of a clouding agent with di(2-ethylhexyl) phthalate (DEHP), a substitute emulsifier-containing compound used in a variety of foods was announced on May 23, 2011. The aims of this study were as follows (1) compare the urine phthalates (PAE) metabolites concentration and estimate the daily intake (DI) of PAEs in pregnant women before and after the tainted food scandal and (2) examine the effect of relatively high PAEs exposure on birth outcome. One-hundred twelve pregnant women in Northern Taiwan participated in this study from March to December 2010, i.e., before the tainted food scandal. After the tainted food scandal, we collected 69, 73, and 180 urine specimens (January 2013 to August 2014) from women whom were in their first, second, and third trimesters of pregnancy, respectively. We measure urinary DEHP metabolite concentrations to estimate the DI of DEHP and the hazard quotient (HQ) of subjects. This was the first study to assess the effects of DEHP-tainted food scandal exposure in pregnant women across the three trimesters of pregnancy. After the tainted food report, the concentrations of urine PAE metabolite were significantly decreased, especially those of DEHP metabolites. Based on different reference limit values, the percentages of pregnant women whose HQ_DEHP value exceeded the limit ranged from 0.53% to 8.93%. Despite this low frequency, the higher ΣPAE exposure during the second trimester may significantly increase the risk of relatively low birth height compared to the lower exposure group (β=-0.63 (-1.20 to -0.06)). Our results support the hypothesis that exposure to relatively high concentrations of DEHP in pregnant Taiwanese women may have an adverse effect on birth outcomes. The percentage of subjects whose exposure level exceeded the exposure limit was low; however, high PAEs exposure appears to be significantly associated with birth outcomes. Therefore, we suggest that reference dose for PAEs should be revised.

Effects of the phthalate exposure during three gestation periods on birth weight and their gender differences: A birth cohort study in China

Phthalate has been widely used as a type of plasticiser in various consuming products in daily life. Recent studies have suggested that prenatal phthalate exposure may have adverse effects on fetal development. We aimed to identify the effects of in utero phthalate exposure on birth weight (BW). We evaluated a birth cohort comprising 3474 pregnant women and their single infants; 3103, 2975 and 2838 urine samples were collected in the first, second and third trimesters, respectively. Phthalate metabolites included monomethyl phthalate (MMP), monoethyl phthalate (MEP), mono-n-butyl phthalate (MBP), monobenzyl phthalate (MBzP), mono-(2-ethylhexyl) phthalate (MEHP), mono-(2-ethyl-5-oxohexyl) phthalate (MEHHP), and mono-(2-ethyl-5-hydroxylhexyl) phthalate (MEOHP), which were analysed in the urine by using high performance liquid chromatography-tandem mass spectrometry. Mixed linear model was used in the statistical analysis. Generally, MMP and MEP exposure during pregnancy was associated with decreased birth weight of infants (MMP, β=-12.192, p=0.009; MEP, β=-11.876, p=0.014). Hierarchical analysis found that MMP and MEOHP exposure was associated with decreased infants' birth weight only in low birth weight groups (MMP, β=-42.538, p=0.005; MEOHP, β=-63.224, p=0.008); MEHP and MEHHP exposure was associated with decreased infants' birth weight in both low birth weight group (MEHP, β=-42.348, p=0.035; MEHHP, β=-50.485, p=0.006) and high birth weight group (MEHP, β=-16.580, p=0.034; MEHHP, β=-18.009, p=0.040), MBP and MEHP exposure were associated with increased infants' birth weight in male NBW group (MBP, β=10.438, p=0.039; MEHP, β=13.223, p=0.017). Moreover, the effect has sex difference. The reduction of birth weight associated with MEHP and MEOHP exposure was stronger in male infants, while MMP and MEP exposure was more significant in female infants.

Children's environmental health based on birth cohort studies of Asia

Numerous studies have explored the associations between environmental pollutants and pediatric health. Recent studies have investigated the issue in Asia, but no systematic review has been published to date. This study aims to elucidate the issue by summarizing relevant epidemiologic evidence for cohorts in Asia, using information from the Birth Cohort Consortium of Asia (BiCCA). Environmental pollutants include mercury, environmental tobacco smoke (ETS), polychlorinated biphenyls (PCB), perfluoroalkyl substances (PFAS) and phthalates. This study sought to classify the effects of such compounds on fetal growth and pregnancy outcomes, neurodevelopment and behavioral problems, allergic disease and immune function and the endocrine system and puberty. These evidences showed ETS has been associated with infant birth weight, children's neurodevelopment and allergy disease; mercury and PCB have been shown to affect children's neurodevelopment; phthalate has effects on endocrine function; PFAS alters children's neurodevelopment, the endocrine system, and the allergic response. However, more consistent and coordinated research is necessary to understand the whole picture of single environmental and/or co-exposure and children's health. Therefore, harmonization and international collaboration are also needed in Asia.